This invention is related to the field of personal identification, and more specifically to the field of automated identification of humans by biometric indicia.
Identification of humans is a goal as ancient as humanity itself. As technology and services have developed in the modern world, human activities and transactions have proliferated in which rapid and reliable personal identification is required. Examples include passport control, computer login control, bank automatic teller machines and other transactions authorization, premises access control, and security systems generally. All such identification efforts share the common goals of speed, reliability, and automation.
The use of biometric indicia for identification purposes requires that a particular biometric factor be unique for each individual, that it be readily measured, and that it be invariant over time. Although many indicia have been proposed over the years, fingerprints are perhaps the most familiar example of a successful biometric identification scheme. As is well known, no two fingerprints are the same, and they do not change except through injury or surgery. It is equally clear, however, that identification through fingerprints suffers from the significant drawback of requiring physical contact with the person. No method exists for obtaining a fingerprint from a distance, nor does any such method appear likely.
A biometric indicator that has been largely ignored by the art is the iris. The iris of every human eye has a unique texture of high complexity, which proves to be essentially immutable over a person's life. No two irises are identical in texture or detail, even in the same person. As an internal organ of the eye the iris is well protected from the external environment, yet it is easily visible even from yards away as a colored disk, behind the clear protective window of the eye's cornea, surrounded by the white tissue of the eye. Although the iris stretches and contracts to adjust the size of the pupil in response to light, its detailed texture remains largely unaltered apart from stretching and shrinking. Such distortions in the texture can readily be reversed mathematically in analyzing an iris image, to extract and encode an iris signature that remains the same over a wide range of pupillary dilations. The richness, uniqueness, and immutability of iris texture, as well as its external visibility, make the iris suitable for automated and highly reliable personal identification. The registration and identification of the iris can be performed using a videocamera without any physical contact, automatically and unobtrusively.
By comparison, other biometrics such as signatures, photographs, fingerprints, voice prints, and retinal blood vessel patterns all have significant drawbacks. Although signatures and photographs are cheap and easy to obtain and store, they are impossible to identify automatically with assurance, and are easily forged. Electronically recorded voice prints are susceptible to changes in a person's voice, and they can be counterfeited. Fingerprints or hand prints require physical contact, and they also can be counterfeited and marred by artifacts.
Iris identification is not to be confused with retinal identification. The iris is easy to see and can readily be imaged with a videocamera. The retina, on the contrary, is hidden deep within the eye, and is difficult to see. Common conditions such as small pupils or cataracts make it difficult or impossible to see the retina, but they do not affect the visibility of the iris.
The only previous attempt to take advantage of these favorable characteristics of the iris for a personal identification system is seen in U.S. Pat. No. 4,641,349, issued to Flom and Safir and entitled "Iris Recognition System," (hereinafter '349). The '349 reference discloses the general concept of using the iris as a method of identification, but it does not describe a developed embodiment of such a system. It does not disclose automatic means to find and isolate the iris within an image, regardless of the location and size of the iris, nor means to extract and encode its texture. Moreover, the '349 reference does not describe any method for computing an identification decision once a list of features has been compiled. In general, a listing of features from two iris images will partially agree and partially disagree, whether or not they originated from the same iris. Generally such lists will also differ in the number of features they comprise. No theoretical or mathematical formulation was provided for basing decisions on such comparisons between incommensurate data sets. Moreover, no method was disclosed for calculating the confidence levels associated with identifications.